I've seen both conventions used in practice. Personally, I've always indicated process flowing directly to the step versus using a node (method 1). IMHO, it is less confusing. I'd say it depends on what your audience may be expecting, as neither method can be misconstrued.

After further study... Unfortunately, I no longer have access to current ISO or NCCLS/CLSI (roughly an American equivalent for clinical sciences) standards. Nevertheless, here are examples of those standards that allow multiple inputs to a process.

There are even examples of multiple inputs to decisions (diamond). It is my understanding that a process can have just one output and any number of inputs. A decision has just two outputs (yes/no; positive/negative; etc.). There is no specification for number of inputs; although, in my experience, I have rarely seen more than two inputs.